TL;DR: the low disk space is expected.
See:http://forum.mikrotik.com/t/chateau-disk-space/145894/1
One chateau I just checked shows V7.7 as:
free-hdd-space: 884.0KiB
total-hdd-space: 15.2MiB
With the following packages loaded:
/system/package/print
Columns: NAME, VERSION
# NAME VERSION
0 zerotier 7.7
1 iot 7.7
2 routeros 7.7
3 gps 7.7